Locks for use in current-day residential structures generally include, inter alia, keyed cylinder locks, keyed deadbolt locks, slidebolts, chain locks, etc. Locks of these types are readily obtainable in hardware and building supply stores for installation in doors and door frames.
Often there are times when it is desirable for a door to be incapable of being unlocked from the outside. This is commonly accomplished by installing a separate secondary lock assembly such as a slide bolt on the door adjacent to the door knob/lock assembly. The slidebolt is manually locked from the inside and cannot be unlocked from the outside with a key. A drawback of installing a slidebolt is that the installation of a secondary lock assembly on the door and door frame can be unsightly. In order to improve appearances, a slide bolt can be incorporated within the door knob/lock assembly. Such a lock assembly is disclosed in U.S. Pat. No. 5,072,978. A drawback of this design is that the size, complexity and cost of the door knob/lock assembly is increased. Accordingly, there is a need for a simple door knob/lock assembly which, when desired, cannot be unlocked from the outside.